Liquid crystal display

ABSTRACT

Each picture element includes first and second sub-picture elements, each of which includes a liquid crystal capacitor and at least one storage capacitor. After a display voltage representing a certain grayscale level has been applied to the respective sub-picture element electrodes of the first and second sub-picture elements, a voltage difference ΔVα is produced between voltages to be applied to the respective liquid crystal capacitors of the first and second sub-picture elements by way of their associated storage capacitor(s). By setting the voltage difference ΔVα value of the blue and/or cyan picture element(s) to be smaller than that of the other color picture elements, shift toward the yellow range at an oblique viewing angle can be minimized.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device andmore particularly relates to a liquid crystal display device with anexcellent viewing angle characteristic.

BACKGROUND ART

Recently, liquid crystal displays (LCDs) have become immensely popularas a big monitor screen for a TV receiver (which will be simply referredto herein as a “TV”).

Those LCDs for use as a big monitor screen for a TV include a so-called“VA mode LCD” that uses a vertical alignment liquid crystal layer (seePatent Document No. 1, for example).

A conventional VA mode LCD has different gamma curves, representing agrayscale-luminance characteristic, when viewed from a frontal viewingangle (i.e., when viewed along a normal to the monitor screen) and whenviewed from an oblique viewing angle (i.e., when the polar angle isgreater than zero degrees). And as the transmittance at an obliqueviewing angle becomes higher than at the frontal viewing angle, theimage may look whitish or excessively bright (which is sometimes calleda “whitening phenomenon”) at the oblique viewing angle. A “multi-pictureelement” technique is one of various means for suppressing such awhitening phenomenon at an oblique viewing angle. According to themulti-picture element technique, one picture element is divided into twoor more sub-picture elements that have mutually different luminances anda grayscale is represented by those two or more sub-picture elements.The multi-picture element technique is also called a “picture elementdivision” technique or an “area grayscale” technique. The multi-pictureelement technique is disclosed in Patent Documents Nos. 2 and 3, forexample, the entire disclosure of which are hereby incorporated byreference.

-   -   Patent Document No. 1: Japanese Patent Application Laid-Open        Publication No. 11-242225    -   Patent Document No. 2: Japanese Patent Application Laid-Open        Publication No. 2004-062146 (corresponding to U.S. Pat. No.        6,958,791)    -   Patent Document No. 3: Japanese Patent Application Laid-Open        Publication No. 2005-55896    -   Patent Document No. 4: Japanese Patent Application Laid-Open        Publication No 2003-270614

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, the present inventors discovered via experiments that the LCDshaving the multi-picture element structures disclosed in PatentDocuments Nos. 2 and 3 have the following problems.

Specifically, when the present inventors fabricated a sample LCD withthe multi-picture element structure and analyzed its viewing anglecharacteristic in detail, the color balance was lost and shifted towardthe yellow range at around an intermediate grayscale (e.g., around145/255 grayscale) at an oblique viewing angle. This is a problem thatoccurs to various degrees not just in the VA mode but also in any otherdisplay mode as well.

Meanwhile, according to the multi-picture element technique disclosed inPatent Document No. 3, the liquid crystal capacitors Clca and Clcb of asub-picture element are capacitively coupled together with a couplingcapacitance Ccp as show in FIG. 5 of Patent Document No. 3. However, themagnitude of the coupling capacitance Ccp is affected by some variationthat inevitably occurs during the manufacturing process. That is to say,even if varied on a color-by-color basis, the magnitude of the couplingcapacitance Ccp is still affected by a variation occurring during themanufacturing process. Consequently, it is difficult to fabricate an LCDwith a good color balance at a high production yield.

It should be noted that Patent Document No. 4 discloses a method forcontrolling a backlight and a method for performing signal processingand correction in response to an input video signal in order tocompensate for the loss of the white balance when an iodine polarizer isused. However, Patent Document No. 4 neither discloses nor suggests theproblems mentioned above.

In order to overcome the problems described above, the present inventionhas an object of providing, first and foremost, a liquid crystal displaydevice that can minimize such a loss of the color balance at an obliqueviewing angle and that can be manufactured at a high production yield.

Means for Solving the Problems

A liquid crystal display device according to the present inventionincludes a plurality of picture elements that are arranged in columnsand rows so as to form a matrix pattern. Each of those picture elementsincludes a liquid crystal layer and a plurality of electrodes forapplying a voltage to the liquid crystal layer. Each of those pictureelements includes a first sub-picture element and a second sub-pictureelement having the ability to apply mutually different voltages to theirliquid crystal layer. At a grayscale level, the first sub-pictureelement has a higher luminance than the second sub-picture element. Eachof the first and second sub-picture elements includes: a liquid crystalcapacitor formed by a counter electrode and a sub-picture elementelectrode that faces the counter electrode through the liquid crystallayer; and at least one storage capacitor, each being formed by astorage capacitor electrode that is electrically connected to thesub-picture element electrode, an insulating layer, and a storagecapacitor counter electrode that is opposed to the storage capacitorelectrode with the insulating layer interposed between them. After adisplay voltage representing a certain grayscale level has been appliedto the respective sub-picture element electrodes of the first and secondsub-picture elements, a voltage difference ΔVα is produced betweenvoltages to be applied to the respective liquid crystal capacitors ofthe first and second sub-picture elements by way of their associatedstorage capacitor(s). In some of the picture elements, the voltagedifference ΔVα changes from one picture element to another.

In one preferred embodiment, the picture elements include a plurality ofcolor picture elements that represent mutually different colors and thatinclude a blue picture element and/or a cyan picture element. Amongthose color picture elements, the ΔVα value of the blue and/or cyanpicture element(s) is the smallest.

In another preferred embodiment, the at least one storage capacitorincludes only one storage capacitor. The counter electrode is a singleelectrode that is provided in common for the first and secondsub-picture elements. The storage capacitor counter electrodes of thefirst and second sub-picture elements are electrically independent ofeach other. And the waveforms of storage capacitor counter voltages tobe supplied through storage capacitor lines that are associated with thestorage capacitor counter electrodes are different between the first andsecond sub-picture elements. In some of the picture elements, thestorage capacitors have different capacitance values. As used herein, if“the storage capacitors of a picture element have different capacitancevalues”, then it means that at least one of the storage capacitors ofthe first and second sub-picture elements has a different storagecapacitance value from the other(s). Normally, the capacitance values oftwo or more storage capacitors in a single picture element are definedto be equal to each other.

In this particular preferred embodiment, the picture elements include aplurality of color picture elements that represent mutually differentcolors and that include a blue picture element and/or a cyan pictureelement. Among those color picture elements, the capacitance value ofthe storage capacitor of the blue and/or cyan picture element(s) is thesmallest.

In a specific preferred embodiment, the color picture elements furtherinclude a red picture element and a green picture element. Supposing thecapacitance values of the storage capacitors of the blue and/or cyanpicture element(s), the green picture element, and the red pictureelement are identified by C_(CS-B), C_(CS-C), C_(CS-G) and C_(CS-R),respectively, the inequality C_(CS-B)≦C_(CS-C)<C_(CS-G)≦C_(CS-R) issatisfied.

In another preferred embodiment, the at least one storage capacitorincludes only one storage capacitor. The counter electrode is a singleelectrode that is provided in common for the first and secondsub-picture elements. The storage capacitor counter electrodes of thefirst and second sub-picture elements are electrically independent ofeach other. And the waveforms of storage capacitor counter voltages tobe supplied through storage capacitor lines that are associated with thestorage capacitor counter electrodes are different between the first andsecond sub-picture elements. In some of the picture elements, the liquidcrystal capacitors have different capacitance values.

In still another preferred embodiment, the liquid crystal display devicefurther includes gate bus lines, source bus lines and TFTs. Each of thefirst and second sub-picture elements includes a TFT that is connectedto the sub-picture element electrode thereof. One of the pictureelements that has the smallest voltage difference ΔVα further includes astorage capacitor that has been formed between the picture element's rowand the gate bus line of its adjacent row.

In yet another preferred embodiment, the liquid crystal display devicefurther includes gate bus lines, source bus lines and TFTs. Each of thefirst and second sub-picture elements includes a TFT that is connectedto the sub-picture element electrode thereof. The gate-drain capacitanceCgd of the TFT of one of the picture elements that has the smallestvoltage difference ΔVα is smaller than that of the TFT of any otherpicture element.

In yet another preferred embodiment, the liquid crystal layer is avertical alignment liquid crystal layer and contributes to conducting adisplay operation in normally black mode.

In yet another preferred embodiment, the at least one storage capacitorincludes two storage capacitors. The counter electrode is a singleelectrode that is provided in common for the first and secondsub-picture elements. The storage capacitor counter electrodes of thetwo storage capacitors of the first sub-picture element are electricallyindependent of each other. And the storage capacitor counter electrodesof the two storage capacitors of the second sub-picture element are alsoelectrically independent of each other.

In this particular preferred embodiment, if the two storage capacitorsof the first sub-picture element are identified by CS1A and CS1B and ifthe two storage capacitors of the second sub-picture element areidentified by CS2A and CS2B, the storage capacitor counter electrodes ofthe storage capacitors CS1A and CS2B are electrically connected to samefirst storage capacitor line. The storage capacitor counter electrodesof the storage capacitors CS1B and CS2A are electrically connected tothe same second storage capacitor line. And the first and second storagecapacitor lines are electrically independent of each other.

In a specific preferred embodiment, if the capacitance values of thestorage capacitors CS1A, CS1B, CS2A and CS2B are identified by Ccs1A,Ccs1B, Ccs2A and Ccs2B, respectively, and if Ccs1α=Ccs1A−Ccs1B andCcs2α=Ccs2A−Ccs2B, some of the picture elements have different Ccs1α orCcs2α.

In a more specific preferred embodiment, the picture elements include aplurality of color picture elements that represent mutually differentcolors and that include a blue picture element and/or a cyan pictureelement. Among those color picture elements, the Ccs1α and Ccs2α valuesof the blue and/or cyan picture element(s) are the smallest.

In another preferred embodiment, if Ccs1β=Ccs1A+Ccs1B andCcs2β=Ccs2A+Ccs2B, the Ccs1β and Ccs2β values remain the same in everypicture element.

Another liquid crystal display device according to the present inventionincludes a plurality of picture elements that are arranged in columnsand rows so as to form a matrix pattern. Each of those picture elementsincludes a liquid crystal layer and a plurality of electrodes forapplying a voltage to the liquid crystal layer. Each of those pictureelements includes a first sub-picture element and a second sub-pictureelement having the ability to apply mutually different voltages to theirliquid crystal layer. At a grayscale level, the first sub-pictureelement has a higher luminance than the second sub-picture element. Eachof the first and second sub-picture elements includes: a liquid crystalcapacitor formed by a counter electrode and a sub-picture elementelectrode that faces the counter electrode through the liquid crystallayer; and at least two storage capacitors, each being formed by astorage capacitor electrode that is electrically connected to thesub-picture element electrode, an insulating layer, and a storagecapacitor counter electrode that is opposed to the storage capacitorelectrode with the insulating layer interposed between them. The counterelectrode is a single electrode that is provided in common for the firstand second sub-picture elements. The storage capacitor counterelectrodes of the at least two storage capacitors of the firstsub-picture element are electrically independent of each other. And thestorage capacitor counter electrodes of the at least two storagecapacitors of the second sub-picture element are also electricallyindependent of each other.

In one preferred embodiment, if two storage capacitors of the firstsub-picture element are identified CS1A and CS1B and if two storagecapacitors of the second sub-picture element are identified by CS2A andCS2B, the storage capacitor counter electrodes of the storage capacitorsCS1A and CS2B are electrically connected to the same first storagecapacitor line. The storage capacitor counter electrodes of the storagecapacitors CS1B and CS2A are electrically connected to the same secondstorage capacitor line. And the first and second storage capacitor linesare electrically independent of each other.

Effects of the Invention

The present invention provides a liquid crystal display device that canminimize such a loss of the color balance (particularly, a shift towardthe yellow range) at an oblique viewing angle and that can bemanufactured at a high production yield. The present invention alsoprovides a liquid crystal display device with a novel structure thatcontributes greatly to achieving such an object.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation illustrating an exemplarymulti-picture element structure.

FIGS. 2( a) and 2(b) show how the chromaticity changes with the viewingangle in a liquid crystal display device having the multi-pictureelement structure shown in FIG. 1. Specifically, FIGS. 2( a) and 2(b)are graphs showing the chromaticity variations in u′ and v′ chromaticitycoordinates with the grayscales at a frontal viewing angle and at anoblique viewing angle (of which the orientation was nine o'clockdirection and the polar angle was 45 degrees).

FIGS. 3( a) and 3(b) are graphs showing how the transmittances withrespect to incoming color light rays in blue, green and red withwavelengths of 450 nm, 550 nm and 650 nm, respectively, changed with thevoltage applied to the liquid crystal layer of a VA mode LCD.Specifically, FIGS. 3( a) and 3(b) are graphs showing thevoltage-transmittance characteristics at the frontal viewing angle andat an oblique viewing angle (of which the orientation was nine o'clockdirection and the polar angle was 45 degrees), respectively.

FIG. 4 shows the grayscale-transmittance characteristics a liquidcrystal display device with the multi-picture element structure at thefrontal viewing angle.

FIG. 5 is a graph showing the grayscale-transmittance characteristics ofthe three primary colors of red (R), green (G) and blue (B) in asituation where a picture element of a liquid crystal display devicewith the multi-picture element structure is viewed from an obliqueviewing angle (of which the orientation is nine o'clock direction andthe polar angle is 45 degrees).

FIG. 6 is a graph showing the voltage-transmittance (V-T) curves ofbright and dark sub-picture elements in a liquid crystal display devicewith the multi-picture element structure.

FIG. 7 is a schematic representation illustrating another exemplarymulti-picture element structure.

FIG. 8 is an equivalent circuit diagram of a picture element with themulti-picture element structure.

Portions (a) through (f) of FIG. 9 schematically show the waveforms ofvoltages to be applied and timings to drive a liquid crystal displaydevice with the multi-picture element structure shown in FIG. 8.

FIG. 10 shows graphs showing the chromaticity variations in u′ and v′chromaticity coordinates with the grayscales at a frontal viewing angleand at an oblique viewing angle (of which the orientation was nineo'clock direction and the polar angle was 45 degrees) in a liquidcrystal display device as a preferred embodiment of the presentinvention.

FIG. 11 is an equivalent circuit diagram of a picture element withanother multi-picture element structure.

FIG. 12 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 200A as another preferredembodiment of the present invention.

FIG. 13 is an equivalent circuit diagram of one of two sub-pictureelements in a liquid crystal display device 300 as still anotherpreferred embodiment of the present invention.

FIG. 14 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 300A as yet anotherpreferred embodiment of the present invention.

FIG. 15 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 400A as yet anotherpreferred embodiment of the present invention.

FIG. 16 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 500A as yet anotherpreferred embodiment of the present invention.

FIG. 17 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 600A as yet anotherpreferred embodiment of the present invention.

FIG. 18A is a schematic cross-sectional view of the liquid crystaldisplay device 600A as viewed on the plane 18A-18A′ shown in FIG. 17.

FIG. 18B is a schematic cross-sectional view of the liquid crystaldisplay device 600A as viewed on the plane 18B-18B′ shown in FIG. 17.

FIG. 18C illustrates, for reference purposes, how the device shown inFIG. 18B looks if the SOG film removed portion is omitted.

FIGS. 19( a) through 19(g) are plan views illustrating the structures ofalternative TFT sections that may be used in a liquid crystal displaydevice according to any of the preferred embodiments of the presentinvention described above.

FIG. 20 is a schematic representation illustrating the picture elementstructure of a liquid crystal display device 700A as yet anotherpreferred embodiment of the present invention.

FIG. 21 is a graph showing the grayscale dependences of ΔVd ofrespective color picture elements in a liquid crystal display deviceaccording to a preferred embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

TFT1, TFT2 thin-film transistor

CS1, CS2 storage capacitor

Clc1, Clc2 liquid crystal capacitor

111-1, 111-2, 111-2 a, 111-2 b sub-picture element electrode

112 gate bus line

113 CS bus line

114 source bus line

116-1, 116-2 TFT

117-1, 117-2 drain extension line

119-1, 119-2, 119-2 a, 119-2 b contact portion

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the configuration and operation of a liquid crystal displaydevice as a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription, the present invention is supposed to be implemented as avertical alignment liquid crystal display device (i.e., a VA mode LCD)that uses a liquid crystal material with negative dielectric anisotropybecause significant effects are achieved by the present invention inthat case. However, the present invention is no way limited to thatspecific preferred embodiment but is also applicable to a TN mode LCD,for example.

Also, in the following description of preferred embodiments, the LCDdisclosed in Patent Document No. 2 is cited as a typical VA mode LCDwith the multi-picture element structure. However, the present inventiondoes not have to be applied to that type of LCD but may also be appliedto any other LCD with the multi-picture element structure.

First of all, it will be described what the present inventors thoughtare the problems with an LCD having the multi-picture element structuredisclosed in Patent Document No. 2.

As described above, when the present inventors fabricated a sample LCDwith the multi-picture element structure and analyzed its viewing anglecharacteristic in detail, the color balance shifted toward the yellowrange at around an intermediate grayscale (e.g., around 145/255grayscale) at an oblique viewing angle.

In the following description, a single picture element is supposed to bedivided into two portions with an equal area (one to one division) asshown in FIG. 1 and a result of chromaticity variation in amulti-picture element structure, in which the bright and darksub-picture elements have an equal area, will be described as anexample. FIGS. 2( a) and 2(b) show the chromaticity variations in u′ andv′ chromaticity coordinates with the grayscales at the frontal viewingangle and at an oblique viewing angle (of which the orientation was nineo'clock direction and the polar angle was degrees), where u′ and v′ arechromaticity coordinates compliant with the CIE 1976 USC standard.

As can be seen from FIGS. 2( a) and 2(b), u′ and v′ did not change somuch with the grayscale at the frontal viewing angle but increasedsignificantly at around 145^(th) grayscale at the oblique viewing angle.As a result, at around the 145^(th) grayscale, the image looked moreyellowish than at any other grayscale.

As a result of researches, the present inventors understand the reasonwhy the image that should have had an intermediate grayscale becameyellowish at the oblique viewing angle as follows. It should be notedthat in this example, a single color display pixel is supposed toconsist of red, green and blue picture elements (i.e., picture elementsin the three primary colors). Naturally, however, the present inventionis in no way limited to this example. But even if a single color displaypixel consisted of four or more color picture elements (multi-primarycolor picture elements), the same statement would apply as long as thepicture elements include a blue picture element. Also, if a cyan pictureelement is included along with, or instead of, the blue picture element,the cyan picture element may be treated just as the blue pictureelement.

FIGS. 3( a) and 3(b) are graphs showing how the transmittances withrespect to incoming color light rays in blue, green and red withwavelengths of 450 nm, 550 nm and 650 nm, respectively, changed with thevoltage applied to the liquid crystal layer of a normally black mode, VAmode LCD. Specifically, FIGS. 3( a) and 3(b) show thevoltage-transmittance characteristics at the frontal viewing angle andat an oblique viewing angle (of which the orientation was nine o'clockdirection and the polar angle was 45 degrees), respectively.

A VA mode LCD utilizes the birefringence effect of its liquid crystallayer, of which the retardation has wavelength dispersion property. Thatis why in a VA mode LCD, the transmittance changes differently accordingto the wavelength of the incoming light. Also, in the normally blackmode, the greater the voltage applied to the liquid crystal layer, thehigher the transmittance with respect to each color light ray as can beseen from FIG. 3( a). It can also be seen that the applied voltage thatmaximized the transmittance to the blue ray was smaller than the appliedvoltage that maximized the transmittance to any other color ray. Andeven after the transmittance to the blue ray reached its maximum value,the transmittances to the other color rays increased as the appliedvoltage was raised. That is why considering normalized transmittances,which are obtained by normalizing the transmittances to the respectivecolor rays with their maximum transmittances, it can be said that onlythe normalized transmittance to the blue ray decreases once the appliedvoltage increasing exceeds a certain value. In white display, if thetransmittance to the blue ray becomes lower than the transmittance toany other color ray, then the color white will shift toward the yellowrange. Also, since the retardation of the liquid crystal layer isapparently larger at an oblique viewing angle than at the frontalviewing angle, the transmittance to the blue ay decreased moresignificantly at the oblique viewing angle than at the frontal viewingangle as can be seen easily by comparing the results of FIGS. 3( a) and3(b) to each other. For that reason, at the oblique viewing angle, theimage becomes yellowish much more sensibly than at the frontal viewingangle.

Next, look at FIG. 4, which shows the grayscale-transmittancecharacteristics of a liquid crystal display device with themulti-picture element structure described above at the frontal viewingangle. In FIG. 4, not only the characteristic of the entire pictureelement but also those of its bright and dark sub-picture elements areshown. Nevertheless, the characteristics of those sub-picture elementsare normalized with the transmittance of the entire picture element. Inother words, the transmittance of the entire picture element isrepresented as the sum of the transmittances of the bright and darksub-picture elements.

As shown in FIG. 4, in a liquid crystal display device with themulti-picture element structure described above, a voltage is applied tothe liquid crystal layers of the respective sub-picture elements suchthat substantially only the bright sub-picture element is lit at lowgrayscales and that the transmittance of the dark sub-picture elementstarts to rise at a certain intermediate grayscale.

If this picture element is viewed from the oblique viewing angle (ofwhich the orientation is nine o'clock direction and the polar angle is45 degrees), the grayscale-transmittance characteristics of the threeprimary colors of red (R), green (G) and blue (B) will be represented bythe curves shown in FIG. 5. The intermediate grayscale pointed to by thearrow in FIG. 5 indicates a point at which the transmittance of thebright sub-picture element of a B picture element (which will be simplyreferred to herein as a “bright sub-picture element B”) gets saturatedwith the increase in grayscale. The transmittance of this brightsub-picture element B gets saturated because the retardation of theliquid crystal layer increases at the oblique viewing angle as describedabove. In this manner, at the oblique viewing angle, the transmittanceof the B picture element decreases at the intermediate grayscaleindicated by the arrow unlike the other R and G picture elements and theimage (that should look gray) around that intermediate grayscale getsyellowish.

As can be seen easily from the foregoing description, in order toovercome the coloring problem, this phenomenon that the transmittance tothe blue ray gets saturated earlier than any other color ray due to theincrease in retardation (see FIG. 3( a)) needs to be suppressed. That isto say, to obtain a structure in which the difference between thevoltages (which will be identified herein by ΔV α) applied at a certaingrayscale to the respective liquid crystal layers of the bright and darksub-picture elements of a particular picture element is distinct fromthe voltage difference of the other picture elements, that voltagedifference may be the smallest in the blue picture element amongmultiple color picture elements.

In a liquid crystal display device with the multi-picture elementstructure of this preferred embodiment, the ΔVα value of the bluepicture element may be made smaller than that of the other color pictureelements by setting the storage capacitance value of the blue pictureelement to be smaller than that of the green and red picture elements.That is to say, among the multiple color picture elements (i.e., primarycolor picture elements) that form a single color display pixel, the bluepicture element may have a smaller storage capacitance value than anyother picture element. If a single color display pixel consists of blue,green and red picture elements as in this example, the capacitancevalues C_(CS-B), C_(CS-G) and C_(CS-R) of the respective storagecapacitors of the blue, green and red picture elements need to satisfythe inequality C_(CS-B)<C_(CS-G)≦C_(CS-R). Optionally, if a structure inwhich C_(CS-G)=C_(CS-R) is adopted, the liquid crystal display devicecan have a simplified structure. In the example to be described below,the two storage capacitors of the sub-picture elements of a singlepicture element are supposed to have an equal capacitance value.However, at least one of the storage capacitance values should satisfythe inequality.

Next, it will be described why the saturation of the transmittance tothe blue ray is prevented by satisfying the inequalityC_(CS-B)<C_(CS-G)≦C_(CS-R).

According to the multi-picture element technique disclosed in PatentDocument No. 2 (each picture element of which is represented by theequivalent circuit diagram of FIG. 8 and all picture elements of whichhave the same capacitance value), a voltage (V+Vm), which is higher byVm than the voltage V to be applied to the liquid crystal layer of aconventional picture element with no multi-picture element structure, isapplied to the liquid crystal layer of one sub-picture element, and avoltage (V−Vm), which is lower than the voltage V by Vm, is applied tothe liquid crystal layer of the other sub-picture element, therebyproducing bright and dark sub-picture elements.

In this case, supposing Vad is the peak-to-peak amplitude of theoscillating waveform of a storage capacitor voltage (CS voltage) to beapplied through a storage capacitor line to a storage capacitor counterelectrode, Ccs is the capacitance value of the storage capacitor of eachsub-picture element, and Clc is the capacitance value of the liquidcrystal capacitor of each sub-picture element, Vm is represented by thefollowing equation:

Vm=(½)·Vad·Ccs/(Clc+Ccs)

This Vad is twice as high as Vad disclosed in Patent Document No. 2.

That is why the voltage-transmittance (V-T) curves of the bright anddark sub-picture elements become as schematically shown in FIG. 6.Specifically, with respect to the V-T curve of a conventional pictureelement with no multi-picture element structure (as indicated by thecentral dotted curve), the V-T curve of the bright sub-picture elementshifts by Vm toward the lower voltage range and that of the darksub-picture element shifts by Vm toward the higher voltage range.

For that reason, if the capacitance values of the respective storagecapacitors of the blue, green and red picture elements are identified byC_(CS-B), C_(CS-G) and C_(CS-R), respectively, the inequalityC_(CS-B)<C_(CS-G)≦C_(CS-R) is preferably satisfied. In that case, Vm ofthe blue picture element becomes smaller than any other color pictureelement, and therefore, the saturation and decrease in the transmittanceof the bright sub-picture element of the blue picture element can beprevented. As a result, the unwanted phenomenon that the image aroundthe intermediate grayscale gets yellowish at the oblique viewing anglecan be suppressed.

It should be noted that if each pixel further includes a cyan pictureelement, then the inequality C_(CS-B)≦C_(CS-C)<C_(CS-G)≦C_(CS-R) ispreferably satisfied, where C_(CS-C) is the capacitance value of thestorage capacitor of the cyan picture element. Also, if each pixelincludes a cyan picture element with no blue picture element, then thecapacitance value C_(CS-C) of the storage capacitor of the cyan pictureelement needs to be smaller than that of the storage capacitor of anyother color picture element (which may be not just a green or redpicture element but also a magenta or yellow picture element). In thatcase, the capacitance values of the storage capacitors of all colorpicture elements but the cyan picture element may be equal to eachother. That is to say, among multiple color picture elements, just theblue or cyan picture element needs to have a smaller storage capacitancevalue than the other color picture elements (which may be not just redand green picture elements). And if blue and cyan picture elements areboth included, settings need to be done so as to satisfy the inequalityC_(CS-B)≦C_(CS-C).

Hereinafter, preferred embodiments of a liquid crystal display deviceaccording to the present invention will be described by way of specificexamples. In the following example, each picture element is supposed tobe equally split into a bright sub-picture element and a darksub-picture element such that these two sub-picture elements have anequal area. The pattern of the multi-picture element structure of theliquid crystal display device of this preferred embodiment shown in FIG.1, but may also be the one shown in FIG. 7. The picture element shown inFIG. 1 includes sub-picture elements #1 and #2 as upper and lower halvesof the picture element. On the other hand, the picture element shown inFIG. 7 includes sub-picture element #1 arranged at the center andsub-picture element #2 that has been split into two halves arranged overand under the sub-picture element #1. However, those two halves of thesub-picture element #2 are electrically equivalent to each other andform a single sub-picture element, too. That is why both of the twotypes of multi-picture element structures shown in FIGS. 1 and 7 arerepresented by the equivalent circuit shown in FIG. 8. And the liquidcrystal display device 100 having the multi-picture element structurerepresented by the equivalent circuit shown in FIG. 8 is driven with theapplication of various voltages shown in FIG. 9. As the details arealready disclosed in Patent Document No. 2, only the gist will be givenbelow.

A single picture element of the liquid crystal display device 100 shownin FIG. 8 includes sub-picture elements #1 and #2. These sub-pictureelements #1 and #2 include liquid crystal capacitors Clc1 and Clc2,respectively, each of which is formed by a liquid crystal layer, acounter electrode to apply a voltage to the liquid crystal layer, and asub-picture element electrode. A counter electrode is a single electrodethat is provided in common for sub-picture elements #1 and #2, and istypically shared by every picture element. A storage capacitor CS1 witha capacitance value Ccs1 and a storage capacitor CS2 with a capacitancevalue Ccs2 are electrically connected in parallel to the liquid crystalcapacitors Clc1 and Clc2, respectively. Each of the storage capacitorsCS1 and CS2 is formed by an insulating layer (such as a gate insulatinglayer) and a storage capacitor counter electrode that faces the storagecapacitor electrode with the insulating layer interposed between them.The storage capacitor electrode is connected to the drain electrode ofthe same TFT as the sub-picture element electrode, while the storagecapacitor counter electrode is connected to a storage capacitor line (CSbus line). In this case, CS bus line #1 connected to the storagecapacitor of sub-picture element #1 and CS bus line #2 connected to thestorage capacitor of sub-picture element #2 are electrically independentof each other. Also, CS bus lines #1 and #2 may be provided for eachpicture element so as to be electrically independent of the other CS buslines. Alternatively, as disclosed in Patent Document No. 2, the numberof electrically independent CS bus lines may be reduced by combining anumber of CS bus lines that supply oscillating voltages with a certainphase relation into a single CS trunk line. In either case, the CS busline voltages (which are also called “CS voltages” or “storage capacitorcounter voltages”) to be supplied to the storage capacitors of two ormore sub-picture elements in a single picture element have mutuallydifferent waveforms.

The sub-picture element electrode of each liquid crystal capacitor Clc1,Clc2 and the storage capacitor electrode of each storage capacitor areconnected to the drain electrode of its associated TFT #1 or #2. Therespective gate electrodes of the TFTs #1 and #2 are connected in commonto the same gate bus line, while the respective source electrodes of theTFTs #1 and #2 are connected in common to the same source bus line.

By supplying the storage capacitor counter voltages to be describedlater through electrically independent CS bus lines to the storagecapacitors of the sub-picture elements with such a relatively simplemulti-picture element structure, the effective voltages applied to theliquid crystal capacitors Clc1 and Clc2 of the respective sub-pictureelements can be either raised or lowered by Vm.

Portions (a) through (f) of FIG. 9 schematically show the waveforms andtimings of respective voltages that are applied to drive the liquidcrystal display device with the multi-picture element structure shown inFIG. 8.

Specifically, portion (a) of FIG. 9 shows the voltage waveform Vs of thesignal voltage supplied through the source bus line (signal line);portion (b) of FIG. 9 shows the voltage waveform Vcs1 of the storagecapacitor voltage supplied through the CS bus line #1; portion (c) ofFIG. 9 shows the voltage waveform Vcs2 of the CS bus line #2; portion(d) of FIG. 9 shows the voltage waveform Vg of the gate bus line;portion (e) of FIG. 9 shows the voltage waveform Vlc1 of the sub-pictureelement electrode of the sub-picture element #1; and portion (f) of FIG.9 shows the voltage waveform Vlc2 of the sub-picture element electrodeof the sub-picture element #2. In FIG. 9, the dashed line indicates thevoltage waveform COMMON (Vcom) of the counter electrode.

Hereinafter, it will be described with reference to portions (a) through(f) of FIG. 9 how the equivalent circuit shown in FIG. 8 operates.

First, at a time T1, the voltage Vg rises from VgL (low) to VgH (high)to turn TFT1 and TFT2 ON simultaneously. As a result, the voltage Vs onthe source bus line is transmitted to the sub-picture element electrodesof the sub-picture elements #1 and #2 to charge the sub-picture elements#1 and #2 with the voltage Vs. In the same way, the storage capacitorsCS1 and CS2 of the respective sub-picture elements are also charged withthe voltage on the source bus line. The voltage Vs on the source busline is a display voltage representing the grayscale to be displayed bythat picture element and is written on an associated picture elementduring a period in which the TFT is ON (and which will be sometimesreferred to herein as a “selected period”).

Next, at a time T2, the voltage Vg on the gate bus line falls from VgHto VgL to turn TFT1 and TFT2 OFF simultaneously and electrically isolatethe sub-picture elements #1 and #2 and the storage capacitors CS1 andCS2 from the source bus line (a period in such a state will sometimes bereferred to herein as a “non-selected period”). It should be noted thatimmediately after the TFTs in ON state have been turned OFF, due to thefeedthrough phenomenon caused by a parasitic capacitance of the TFT1 andTFT2, for example, the voltages Vlc1 and Vlc2 applied to the respectivesub-picture element electrodes decrease by approximately the samevoltage Vd to:

Vlc1=Vs−Vd

Vlc2=Vs−Vd

respectively. Also, in this case, the voltages Vcs1 and Vcs2 on the CSbus lines are:

Vcs1=Vcom−(½)Vad

Vcs2=Vcom+(½)Vad

respectively. That is to say, the waveforms of these exemplary voltagesVcs1 and Vcs2 on the CS bus lines are square waves, of which the (full)amplitude is Vad, of which the phases are opposite to each other (i.e.,different from each other by 180 degrees) and which have a duty ratio ofone to one.

Next, at a time T3, the voltage Vcs1 on the CS bus line #1 connected tothe storage capacitor CS1 rises from Vcom−(½)Vad to Vcom+(½)Vad and thevoltage Vcs2 on the CS bus line #2 connected to the storage capacitorCS2 falls from Vcom+(½)Vad to Vcom−(½)Vad. That is to say, thesevoltages Vcs1 and Vcs2 both change by Vad. As the voltages on the CS buslines #1 and #2 change in this manner, the voltages Vlc1 and Vlc2applied to the respective sub-picture element electrodes change into:

Vlc1=Vs−Vd+K×Vad

Vlc2=Vs−Vd−K×Vad

respectively, where K=Ccs/(Clc(V)+Ccs).

Next, at a time T4, Vcs1 falls from Vcom+(½)Vad to Vcom−(½)Vad and Vcs2rises from Vcom−(½)Vad to Vcom+(½)Vad. That is to say, these voltagesVcs1 and Vcs2 both change by Vad again. In this case, Vlc1 and Vlc2 alsochange from

Vlc1=Vs−Vd+K×Vad

Vlc2=Vs−Vd−K×Vad

into

Vlc1=Vs−Vd

Vlc2=Vs−Vd

respectively.

Next, at a time T5, Vcs1 rises from Vcom−(½)Vad to Vcom+(½)Vad and Vcs2falls from Vcom+(½)Vad to Vcom−(½)Vad. That is to say, these voltagesVcs1 and Vcs2 both change by Vad again. In this case, Vlc1 and Vlc2 alsochange from

Vlc1=Vs−Vd

Vlc2=Vs−Vd

into

Vlc1=Vs−Vd+K×Vad

Vlc2=Vs−Vd−K×Vad

respectively.

After that, every time a period of time that is an integral number oftimes as long as one horizontal write period 1H has passed, the voltagesVcs1, Vcs2, Vlc1 and Vlc2 alternate their levels at the times T4 and T5.The intervals between the repeated changes at T4 and T5 may beappropriately determined to be one, two, three or more times as long as1H in view of the method for driving the liquid crystal display device(such as the method of inverting the polarity) and the display status(such as the degree of flicker or roughness of the image on the screen).Such alternate level changes are continued until the picture element isrewritten next time (i.e., until a point in time equivalent to T1arrives). Consequently, the effective values of the voltages Vlc1 andVlc2 applied to the sub-picture element electrodes become:

Vlc1=Vs−Vd+K×(½)Vad

Vlc2=Vs−Vd−K×(½)Vad

respectively.

Therefore, the effective voltages V1 and V2 applied to the liquidcrystal layers of the sub-picture elements #1 and #2 become:

V1=Vlc1−Vcom

V2=Vlc2−Vcom

That is to say,

V1=Vs−Vd+K×(½)Vad−Vcom

V2=Vs−Vd−K×(½)Vad−Vcom

respectively.

As a result, the difference ΔV12 (=V1−V2, which will be sometimesreferred to herein as “ΔVα”) between the effective voltages applied tothe liquid crystal layers of the sub-picture element #1 and #2 becomes

ΔV12=K×Vad

(where K=Ccs/(Clc+Ccs)). It should be noted that the voltage dependenceof Clc is not taken into consideration in this example.

Hereinafter, a specific example of a liquid crystal display deviceaccording to this preferred embodiment, in which Ccs/Clc is set to be0.85 and Vad is defined to be 2.5 V, will be described.

Suppose the respective storage capacitors of red, green and blue pictureelements have capacitance values C_(CS-R), C_(CS-G), and C_(CS-B),respectively. In this case, C_(CS-R)=C_(CS-G) is supposed to besatisfied and the parameter X representing the ratio of the capacitancevalue of the storage capacitor of the blue picture element to that ofthe storage capacitors of the other color picture elements is supposedto be given by X=C_(CS-B)/C_(CS-G)=C_(CS-B)/C_(CS-R).

The variations in the chromaticity represented by u′ and v′ chromaticitycoordinates with the grayscale at the frontal viewing angle and at anoblique viewing angle (of which the orientation was nine o'clockdirection and the polar angle was 45 degrees) in a situation where X wasset to be 1.00, 0.68, 0.56 or 0.45 are shown in FIGS. 10( a) through10(d). Specifically, FIGS. 10( a) and 10(b) are graphs showing thegrayscale dependences of u′ and v′ at the frontal viewing angle, whileFIGS. 10( c) and 10(d) are graphs showing the grayscale dependences ofu′ and v′ at the oblique viewing angle.

As can be seen from FIGS. 10( a) and 10(b), at the frontal viewingangle, the grayscale dependence remained the same in both u′ and v′ nomatter how much the X value changed. On the other hand, as can be seenfrom FIGS. 10( c) and 10(d), at the oblique viewing angle, the smallerthe X value, the more significantly u′ and v′ decreased in the vicinityof 140/255 grayscale. Among other things, v′ changed particularlysteeply and the shift toward the yellow range at the oblique viewingangle could be reduced effectively by decreasing the X value (i.e.,X<1). The best X value for the liquid crystal display device of thisexample would be 0.56 according to the results shown in FIG. 10.

In the liquid crystal display device of this example, the best X valuewas 0.56. However, if the CS oscillating voltage Vad, the storagecapacitance Ccs, and/or the liquid crystal capacitance Clc change(s),then the best X value will also change. That is why the best X value maybe defined appropriately in that case. Also, in this example,C_(CS-G)=C_(CS-R) is supposed to be satisfied. However,C_(CS-G)<C_(CS-R), the color shift caused by the earlier saturation ofthe green ray than the red ray in the voltage-transmittance curves shownin FIGS. 3( a) and 3(b) can be minimized.

Also, if the multi-picture element structure disclosed in PatentDocument No. 2 is adopted, a predetermined effective voltage differencecan be produced between sub-picture elements by adjusting the Vad valueirrespective of the variation that should occur between respectiveliquid crystal display devices being manufactured and unlike themulti-picture element structure disclosed in Patent Document No. 4. Inthe example described above, the amplitudes of the two CS bus linevoltages Vcs1 and Vcs2 are both supposed to be Vad. However, thoseamplitudes may also be defined independently of each other.

In a liquid crystal display device that uses TFTs, the voltage at asub-picture element electrode should decrease by ΔVd by nature when thegate voltage Vg falls from VgH to VgL as shown in FIG. 9. In this case,the ΔVd value depends on the ratio of the parasitic capacitance Cgdbetween the gate electrode and drain electrode of a TFT to the sum ofthe capacitances of all capacitors that are connected to the drainelectrode (namely, the liquid crystal capacitor Clc, storage capacitorCcs and other parasitic capacitors). Normally, Cgd, Clc and Ccs aredominant capacitances and the ΔVd value can be given byΔVd=Cgd/(Clc+Ccs). That is why if only the Ccs values are simply changedas described above to obtain a desired ΔVα on a color picture elementbasis, then the ΔVd value should also be different from one colorpicture element to another. If the ΔVd values are different betweenrespective color picture elements, the average of the voltages to beapplied to the respective liquid crystal layers of the color pictureelements (i.e., the DC level) will also vary. In that case, in a typicalconfiguration in which a counter electrode is provided in common for allpicture elements, the DC voltage components applied to the liquidcrystal layers of all picture elements could not be reduced sufficientlyeven if the counter voltage was regulated. And if the DC voltagecomponents applied to the liquid crystal layers were high, then thedisplay quality or reliability would be affected. That is a problem.

Such a problem could be avoided by providing counter electrode for eachgroup of color picture elements of the same color and by regulating thecounter voltage applied to the counter electrode associated with eachgroup of color picture elements. Naturally, if the electricalconfiguration of only blue picture elements (and/or cyan pictureelements) should be different from that of the other color pictureelements, then a first counter electrode associated with a group of bluepicture elements (and/or cyan picture elements) and a second counterelectrode associated with groups of picture elements of the other colorsshould be provided and the counter voltages should be regulated so as tocompensate for ΔVd for the first and second counter electrodesindependently of each other.

If such a measure was taken, however, the counter electrode should besplit into at least two sections and respectively predetermined voltages(i.e., counter voltages) should be applied to those two sections of thecounter electrode independently of each other, thus complicating theconfiguration of the liquid crystal display device and increasing itscost.

Thus, to overcome such a problem, a liquid crystal display device thatcan sufficiently reduce the DC voltage components applied to the liquidcrystal layer of every color picture element without complicating thestructure too much to avoid that increase in cost will be described asanother preferred embodiment of the present invention.

FIG. 11 is an equivalent circuit diagram representing a picture elementwith a multi-picture element structure of a liquid crystal displaydevice 200 as another preferred embodiment of the present invention.Unlike the picture element shown in FIG. 8, each of the sub-pictureelements #1 and #2 of the picture element shown in FIG. 11 has twostorage capacitors. The respective storage capacitor counter electrodesof the two storage capacitors of sub-picture element #1 are electricallyindependent of each other, and those of the two storage capacitors ofsub-picture element #2 are also electrically independent of each other.

As shown in FIG. 11, sub-picture element #1 includes storage capacitorsCS1A and CS1B and sub-picture element #2 includes storage capacitorsCS2A and CS2B. The storage capacitor counter electrodes of the storagecapacitors CS1A and CS2B are electrically connected to the same CS busline #1, the storage capacitor counter electrodes of the storagecapacitors CS1B and CS2A are electrically connected to the same CS busline #2, and those CS bus lines #1 and #2 are electrically independentof each other. In this example, square waves, of which the phases aredifferent from each other by 180 degrees and of which the amplitude isVad as shown in FIG. 9, are used as the CS voltages.

Suppose the capacitance values of these storage capacitors CS1A, CS1B,CS2A and CS2B are identified by Ccs1A, Ccs1B, Ccs2A and Ccs2B,respectively. In that case, as the CS voltages supplied through the CSbus lines #1 and #2 have mutually opposite phases, the effective storagecapacitance value Ccs1α of sub-picture element #1 is given byCcs1A-Ccs1Band the effective storage capacitance value Ccs2α ofsub-picture element #2 is given by Ccs2A-Ccs2B. As a result, by settingCcs1α or Ccs2α of blue and/or cyan picture element(s) among multiplecolor picture elements (i.e., primary color picture elements) that forma single color display pixel to be smaller than that of the other colorpicture elements as described above, the ΔVα value of the blue and/orcyan picture element(s) can be smaller than that of the other colorpicture elements.

In this case, supposing Ccs1β=Ccs1A+Ccs1B and Ccs2β=Ccs2A+Ccs2B, if theCcs1β and Ccs2β values remain almost the same in every picture element,then the problem that would be caused if ΔVd is different from one colorpicture element to another can be avoided. That is to say, by making theCcs1β and Ccs2β values substantially the same in every picture element,TFTs #1 and #2 of every picture element can have the same design, andtherefore, the ΔVd values can also be substantially the same in everypicture element. With such a configuration, there is no need to performthe additional process step of patterning the counter electrode or togenerate a plurality of counter voltages. And such a configuration isrealized just by changing the patterns of a photomask for use in themanufacturing process of TFTs. As a result, the increase in cost can beminimized, too.

As described above, normally, ΔVd is calculated by Cgd/(Clc+Ccs) but(since the dielectric constant of the liquid crystal layer varies asliquid crystal molecules with dielectric anisotropy change theirorientations) Clc changes with the voltage applied to the liquid crystallayer. That is why to make ΔVd substantially the same in every pictureelement and at every grayscale, the ratio of Ccs to Clc (which will besometimes simply referred to herein as a “Ccs ratio”) is preferablysubstantially constant in every picture element.

On top of that, the liquid crystal display device 200 shown in FIG. 11can be designed more flexibly than the liquid crystal display device 100shown in FIG. 8.

In the configuration shown in FIG. 8, the ΔVα value changesproportionally to the Ccs1 value. That is why to reduce the ΔVα value toone-tenth, the Ccs1 value also needs to be reduced to one-tenth in theliquid crystal display device 100 shown in FIG. 8. As the capacitancevalue of a storage capacitor depends on the area of the electrode, theelectrode's area should also be reduced to one-tenth if the Ccs1 valueshould be reduced to one-tenth. This is not beneficial considering theelectrode patterning precision currently available and the eventualproduction yield. That is to say, the magnitude of the variation in asituation where the ΔVα value of a blue picture element should bereduced in the liquid crystal display device 100 shown in FIG. 8 (i.e.,the difference from the ΔVα value of the other color picture elements)would be restricted by the patterning precision or the production yield.In other words, the flexibility of design would decrease. It isnaturally possible to increase the ΔVα value of the other color pictureelements to relax such a restriction. However, since the ΔVα value isessentially determined from the viewpoint of the viewing anglecharacteristic, such a measure should not be adopted. On the other hand,in the liquid crystal display device 200 shown in FIG. 11, the ΔVα valueis determined based on the difference between the capacitance values ofthe storage capacitors CS1A and CS1B. That is to say, the ΔVα value doesnot directly depend on the capacitance values of the storage capacitorsCS1A and CS1B themselves, and therefore, is free from the restriction onthe patterning precision or production yield. For example, to reduce theΔVα value of the blue picture element to one-tenth, the color pictureelements other than the blue picture element may have capacitance valuesof 100 pF and 50 pF in their respective storage capacitors CS1A and CS1B(i.e., CS1A−CS1B=50 pF) and the blue picture element may havecapacitance values of 55 pF and 50 pF in their respective storagecapacitors CS1A and CS1B (i.e., CS1A−CS1B=5 pF). That is to say, thecapacitance values of the storage capacitors CS1A and CS1B of the bluepicture element can be close to those of the other color pictureelements, and the ΔVα value can be set flexibly on a color-by-colorbasis. Furthermore, as described above, Ccs1β and Ccs2β are morepreferably substantially the same in every picture element.Specifically, the blue picture element more preferably satisfiesCS1A=77.5 pF and CS1B=72.5 pF, of which the sum is equal to the sum ofthe capacitance values of the storage capacitors CS1A and CS1B (=150 pF)in every picture element.

The liquid crystal display device 200 shown in FIG. 11 can be used tonot only minimize the shift in color balance at an oblique viewing angleas described above but also increase the precision of setting the ΔVαvalue as well.

The ΔVα value depends on the product of the capacitance value of astorage capacitor and the amplitude of the CS voltage supplied from anexternal circuit. In the liquid crystal display device 100 shown in FIG.8, to increase the precision of setting the storage capacitance value,the storage capacitance value needs to be a relatively large value. Inthat case, the CS voltage supplied from an external circuit will havedecreased amplitude and the precision of setting the amplitude of the CSvoltage will decrease. Conversely, to increase the precision of settingthe amplitude of the CS voltage by increasing the amplitude of the CSvoltage supplied from the external circuit, the storage capacitancevalue should be reduced to a smaller value, and therefore, the precisionof setting the storage capacitance value will decrease. In contrast,with the configuration shown in FIG. 11, the storage capacitance valuecan be set to be relatively large value with the amplitude of thevoltage supplied from an external circuit kept sufficient large. As aresult, the precision of setting the ΔVα value can be increased.

Furthermore, by electrically connecting the storage capacitor counterelectrodes of the storage capacitors CS1A and CS2B to the same CS busline #1 and the storage capacitor counter electrodes of the storagecapacitors CS1B and CS2A to the same CS bus line #2 (which iselectrically independent of CS bus line #1), respectively, as shown inFIG. 11, the number of electrically independent CS bus lines can be cutdown, which is also beneficial.

FIG. 12 illustrates a picture element structure for a liquid crystaldisplay device 200A as a preferred embodiment of the present invention.The equivalent circuit of the liquid crystal display device 200A is thesame as that of the liquid crystal display device 200 shown in FIG. 11.In FIG. 12, illustrated schematically are the structure of two pictureelements that are located at the intersection between the m^(th) row andn^(th) column and at the intersection between the m^(th) row and(n+1)^(th) column on the TFT substrate, among multiple picture elementsthat are arranged in column and rows. The picture element at theintersection between the m^(th) row and n^(th) column is either a redpicture element or a green picture element, while the picture element atthe intersection between the m^(th) row and (n+1)^(th) column is a bluepicture element. In the following description, any pair of componentsshown in multiple drawings and having substantially the same functionwill be identified by the same reference numeral. And once a componenthas been described, the description of its counterpart will be omittedherein to avoid redundancies.

In this liquid crystal display device 200A, each picture element Pincludes a first sub-picture element SP1 and a second sub-pictureelement SP2 a and SP2 b, of which the liquid crystal layers can besupplied with mutually different voltages, and at a certain grayscale,the first sub-picture element has a higher luminance than the secondsub-picture element. The second sub-picture element includes secondsub-picture element portions SP2 a and SP2 b, which are arranged so asto interpose the first sub-picture element SP1 between them. That is tosay, this liquid crystal display device 200A has the multi-pictureelement structure shown in FIG. 7. However, the area of the secondsub-picture element (i.e., the combined area of the second sub-pictureelement portions SP2 a and SP2 b) is approximately three times as largeas that of the first sub-picture element SP1. In this case, the secondsub-picture element portions SP2 a and SP2 b are located spatially apartfrom each other, but are electrically equivalent to each other, have thesame voltage applied to their liquid crystal layers, and also exhibitthe same electro-optical characteristic (i.e., V-T characteristic). Thatis why from the viewpoint of V-T characteristic, these secondsub-picture element portions SP2 a and SP2 b form a single sub-pictureelement (i.e., the second sub-picture element). That is to say, thepicture element P exhibits two different types of V-T characteristicsand can also be regarded as having a structure in which a single pictureelement has been split into first and second sub-picture elements SP1and SP2. In the following description, these second sub-picture elementportions SP2 a and SP2 b will be collectively referred to herein as the“second sub-picture element SP2” for the sake of simplicity.

As shown in FIG. 12, the first sub-picture element SP1 is arranged inthe area defined by a first sub-picture element electrode 111-1, whilethe second sub-picture element portions SP2 a and SP2 b are arranged inthe areas defined by second sub-picture element electrode halves 111-2 aand 111-2 b.

Now look at the picture element P located at the intersection betweenthe m^(th) row and n^(th) column (which will be simply referred toherein as an (m, n) picture element). The (m, n) picture element isdriven by TFTs 116-1 and 116-2 that are connected to a gate bus line112(m) and a source bus line 114(n). The drain of the TFT 116-1 isconnected to the first sub-picture element electrode 111-1 at a contactportion 119-1 by way of a drain extension line 117-1. On the other hand,the drain of the TFT 116-2 is connected to the second sub-pictureelement electrode half 111-2 a at a contact portion 119-2 a by way of adrain extension line 117-2 and is also connected to the secondsub-picture element electrode half 111-2 b at a contact portion 119-2 bby way of the drain extension line 117-2. The sub-picture elementelectrodes 111-1, 111-2 a and 111-2 b, along with the liquid crystallayer (not shown) and the counter electrode (not shown, either) opposedto the electrodes through the liquid crystal layer, form liquid crystalcapacitors. Specifically, the sub-picture element electrode 111-1 formsClc1 shown in FIG. 11 and the sub-picture element electrodes 111-2 a and111-2 b form Clc2 shown in FIG. 11.

In this example, the source bus line 114(n) includes two main lines thatrun in the column direction and a bridge portion that connects those twomain lines together. One of the two main lines of the source bus line114(n) overlaps with the sub-picture element electrodes 111-1, 111-2 aand 111-2 b on the n^(th) column, while the other main line overlapswith the sub-picture element electrodes on the (n−1)^(th) column. Inthis case, to reduce the parasitic capacitance Csd between the sourcebus line 114(n) and the sub-picture element electrodes sufficiently, aninterlayer dielectric film of a resin is provided between them. In otherwords, by providing such an interlayer dielectric film, the sub-pictureelement electrodes can be arranged so as to overlap with the source busline 114(n) and the aperture ratio of the pixel can be increased as aresult.

The TFTs 116-1 and 116-2 have a bottom-gate structure and each include:a gate electrode, which is provided as an extended portion of the gatebus line 112(m); a semiconductor layer (not shown), which is arrangedover the gate electrode; and source/drain electrodes, which are arrangedin the source region of the semiconductor layer. The source electrode isprovided as an extended portion of the source bus line 114(n). The drainelectrodes of the TFTs 116-1 and 116-2 form an integral part of thedrain extension lines 117-1 and 117-2, respectively. Furthermore, theinterlayer dielectric film is provided so as to cover all of thesemembers. And the sub-picture element electrodes 111-1, 111-2 a and 111-2b are arranged on the interlayer dielectric film. At the contactportions 119-1, 119-2 a and 119-2 b that are arranged to fill thecontact holes that have been cut through the interlayer dielectric film,the drain extension lines 117-1 and 117-2 are connected to thesub-picture element electrodes 111-1, 111-2 a and 111-2 b.

Next, the configuration of the storage capacitors of the (m, n) pictureelement will be described. In this example, the (m, n) picture elementmay be either a red picture element or a green picture element.

Through the picture elements on the m^(th) row, two CS bus lines (i.e.,storage capacitor lines) 113-1 and 113-2 run. The CS bus lines 113-1 and113-2 respectively correspond to CS bus lines #1 and #2 shown in FIG.11.

The sub-picture element SP1 includes two storage capacitors CS1A andCS1B. The storage capacitor CS1A is arranged at an intersection betweenthe drain extension line 117-1 and the CS bus line 113-1. On the otherhand, the storage capacitor CS1B is arranged in an area where anextended portion 117-1E of the drain extension line 117-1 and abroadened portion of the CS bus line 113-1 overlap with each other. Bothof the CS bus lines 113-1 and 113-2 are made of the same conductivelayer as the gate bus line 112(m) and are covered with the gateinsulating film (not shown). The dielectric layers of the storagecapacitors CS1A and CS1B are both gate insulating films and thecapacitance values thereof are both proportional to the areas of theelectrodes. In this example, the capacitance value of the storagecapacitor CS1A is smaller than that of the storage capacitor CS1B asshown in FIG. 12.

The sub-picture element SP2 includes two storage capacitors CS2A andCS2B. The storage capacitor CS2A is arranged at an intersection betweenthe drain extension line 117-2 and the CS bus line 113-2. On the otherhand, the storage capacitor CS2B is arranged in an area where anextended portion 117-2E of the drain extension line 117-2 and abroadened portion of the CS bus line 113-1 overlap with each other. Thedielectric layers of the storage capacitors CS2A and. CS2B are both gateinsulating films and the capacitance values thereof are bothproportional to the areas of the electrodes. In this example, thecapacitance value of the storage capacitor CS2A is smaller than that ofthe storage capacitor CS2B as shown in FIG. 12.

Next, the configuration of the storage capacitors of the (m, n+1)picture element (.e., a blue picture element) will be described.

The sub-picture element SP1 of the blue picture element includes twostorage capacitors CS1A and CS1B. The storage capacitor CS1A is arrangedin an area where a first extended portion 117-1E1 of the drain extensionline 117-1 and a broadened portion of the CS bus line 113-1 overlap witheach other. On the other hand, the storage capacitor CS1B is arranged inan area where a second extended portion 117-1E2 of the drain extensionline 117-1 and a broadened portion of the CS bus line 113-2 overlap witheach other and at an intersection between the drain extension line 117-1and the CS bus line 113-2. In this example, the capacitance value of thestorage capacitor CS1A is larger than that of the storage capacitor CS1Bas shown in FIG. 12.

The sub-picture element SP2 of the blue picture element includes twostorage capacitors CS2A and CS2B. The storage capacitor CS2A is arrangedin an area where an extended portion 117-2E1 of the drain extension line117-2 and a broadened portion of the CS bus line 113-2 overlap with eachother. On the other hand, the storage capacitor CS2B is arranged in anarea where a second extended portion 117-2E2 of the drain extension line117-2 and a broadened portion of the CS bus line 113-1 overlap with eachother and at an intersection between the drain extension line 117-2 andthe CS bus line 113-1. In this example, the capacitance value of thestorage capacitor CS2A is larger than that of the storage capacitor CS2Bas shown in FIG. 12.

In this manner, the connectivity between the storage capacitors CS1A andCS1B and their associated CS bus lines and the magnitudes of thecapacitance values of the storage capacitors CS1A and CS1B in the (m, n)picture element turn over in the (m, n+1) picture element. Thisarrangement is adopted to cope with a drive mode in which the polaritiesof write voltages (i.e., the polarities of the voltages supplied throughthe source bus line 114 with reference to the counter voltage (that iscalled a “display signal voltage”)) invert between the (m, n) and (m,n+1) picture elements. Such a drive mode is sometimes called a “dotinversion drive”.

In each of the (m, n) and (m, n+1) picture elements, the storagecapacitor counter electrodes of the storage capacitors CS1A and CS2B areelectrically connected to the same CS bus line 113-1, while the storagecapacitor counter electrodes of the storage capacitors CS1B and CS2A areelectrically connected to the same CS bus line 113-2. Suppose the squarewaves, of which the phases are different from each other by 180 degreesand which have amplitude Vad as shown in FIG. 9, are supplied as the CSvoltages through the CS bus lines 113-1 and 113-2 as in the exampledescribed above and the capacitance values of the storage capacitorsCS1A, CS1B, CS2A and CS2B are identified by Ccs1A, Ccs1B, Ccs2A andCcs2B, respectively. In that case, since the phases of the CS voltagessupplied through the CS bus lines 113-1 and 113-2 are opposite to eachother, the effective storage capacitance value Ccs1α for the sub-pictureelement SP1 becomes Ccs1A-Ccs1B and the effective storage capacitancevalue Ccs2α for the sub-picture element SP2 becomes Ccs2A-Ccs2B. That iswhy as already described with reference to FIG. 11, by setting the Ccs1αor Ccs2α value of the blue picture element among multiple color pictureelements that form a single color display pixel (.e., picture elementsin the three primary colors of R, G and B in this example) to be smallerthan that of the other color picture elements, the ΔVα value of the bluepicture element can be smaller than that of the other color pictureelements. In the example illustrated in FIG. 12, by increasing thecapacitance values of the blue picture element, i.e., Ccs1B and Ccs2B ofthe (m, n+1) picture element, Ccs1α and Ccs2α are decreased.

In this case, supposing Ccs1β=Ccs1A+Ccs1B and Ccs2β=Ccs2A+Ccs2B, theCcs1β and Ccs2β values remain almost the same in every picture elementas shown in FIG. 12. That is why the problem that would occur if ΔVdwere different from one color picture element to another can be avoided.Specifically, both of the (m, n) and (m, n+1) picture elements have thesame Ccs1β and Ccs2β values.

Furthermore, in the example illustrated in FIG. 12, the ratio of thecapacitance of the liquid crystal capacitor Clc1 to the storagecapacitance Ccsβ1 in the sub-picture element SP1 and the ratio of thecapacitance of the liquid crystal capacitor Clc2 to the storagecapacitance Ccsβ2 in the sub-picture element SP2 are substantially equalto each other. Since the liquid crystal layers of the sub-pictureelements SP1 and SP2 have the same thickness, the liquid crystalcapacitance of each sub-picture element is proportional to the area ofits associated sub-picture element electrode. And since the area of thesub-picture element SP2 is roughly three times as large as that of thesub-picture element SP1, the liquid crystal capacitance of thesub-picture element SP2 will also be approximately three times as largeas that of the sub-picture element SP1. That is why by setting thecapacitance value Ccs2β of the storage capacitor of the sub-pictureelement SP2 to be approximately three times as large as the capacitancevalue Ccsβ1 of the storage capacitor of the sub-picture element SP1, theratio of the capacitance value of the liquid crystal capacitor Clc1 tothe storage capacitance Ccsβ1 in the sub-picture element SP1 is madeapproximately equal to the ratio of the capacitance value of the liquidcrystal capacitor Clc2 to the storage capacitance Ccsβ2 in thesub-picture element SP2.

Furthermore, in the example illustrated in FIG. 12, the drain extensionlines 117-1 and 117-2 and the drain extension lines' extended portions117-1E, 117-2E, 117-1E1, 117-1E2, 117-2E1 and 117-2E2 are arranged suchthat the blue picture element (i.e., (m, n+1) picture element in thisexample) and the other picture elements (i.e., (m, n) picture element inthis example) have apertures (i.e., openings to pass the incoming light)of the same shape. By making the shapes of the apertures of all pictureelements substantially the same in this manner, the uniformity ofdisplay can be increased.

Hereinafter, a liquid crystal display device as still another preferredembodiment of the present invention will be described with reference toFIGS. 13 and 14.

FIG. 13 is an equivalent circuit diagram of one of the two sub-pictureelements of a single picture element in a liquid crystal display device300 having a dual picture element structure.

As already described with reference to FIG. 8, if the capacitance valueof the storage capacitor of the blue picture element is reduced suchthat the blue picture element has the smallest ΔVα value, then the bluepicture element will have different ΔVd from the other color pictureelements. Thus, in this liquid crystal display device 300, to compensatefor the decrease in the capacitance value of the storage capacitor ofthe blue picture element, a gate-drain capacitor CGD-1 is formed usingthe gate bus line on an adjacent row. In this example, as to a bluepicture element belonging to the m^(th) row, CGD-1 is formed with thegate bus line on the (m−1)^(th) row. However, the present invention isin no way limited to this specific example. Alternatively, CGD-1 mayalso be formed using the gate bus line on (m+1)^(th) row. If such acompensating gate-drain capacitor CGD-1 (of which the capacitance valueis identified by C_(CGD-1)) is formed with a gate bus line at anOFF-state potential in this manner, then ΔVd=Cgd/(Clc+Ccs+C_(CGD-1))will be satisfied. Thus, by regulating C_(CGD-1) (i.e., by ironing outthe difference in capacitance value between the storage capacitor of theblue picture element and those of the other color picture elements),every color picture element can have the same ΔVd value.

FIG. 14 illustrates a picture element structure for a liquid crystaldisplay device 300A as a preferred embodiment of the present invention.The equivalent circuit of the liquid crystal display device 300A is thesame as that of the liquid crystal display device 300 shown in FIG. 13.In FIG. 14, illustrated schematically are the structure of two pictureelements that are located at the intersection between the m^(th) row andn^(th) column and at the intersection between the m^(th) row and(n+1)^(th) column on the TFT substrate, among multiple picture elementsthat are arranged in column and rows. The picture element at theintersection between the m^(th) row and n^(th) column is either a redpicture element or a green picture element, while the picture element atthe intersection between the m^(th) row and (n+1)^(th) column is a bluepicture element. In this liquid crystal display device 300A, eachpicture element P includes a first sub-picture element SP1 and a secondsub-picture element SP2. That is to say, this liquid crystal displaydevice 300A has the multi-picture element structure shown in FIG. 1 andthe ratio in the area of the first sub-picture element SP1 to the secondsub-picture element SP2 is one to one.

Unlike the liquid crystal display device 200A shown in FIG. 12, eachsub-picture element of the liquid crystal display device 300A has onlyone storage capacitor. Specifically, the sub-picture element SP1includes only a storage capacitor CS1A between the CS bus line 113-1 andthe extended portion 117-1E of the drain extension line 117-1 but has nostorage capacitors with the CS bus line 113-2. On the other hand, thesub-picture element SP2 includes only a storage capacitor CS2A betweenthe CS bus line 113-2 and the extended portion 117-2E of the drainextension line 117-2 but has no storage capacitors with the CS bus line113-1. In this respect, the liquid crystal display device 300A has asimpler configuration than the liquid crystal display device 200A.

In the liquid crystal display device 300A, by setting the capacitancevalues (or the areas) of the storage capacitors CS1A and CS2A of theblue picture element (i.e., the (m, n+1) picture element) to be smallerthan those of the storage capacitors CS1A and CS2A of the other colorpicture element (i.e., the (m, n) picture element) as described above,the ΔVα value of the blue picture element can be smaller than that ofthe other color picture element.

Look at the blue picture element (i.e., the (m, n+1) picture element)now. The drain extension line 117-1 includes a first extended portion117-1E1 that forms the storage capacitor CS1A of the sub-picture elementSP1 and a second extended portion 117-1E2 that overlaps with a gate busline 112(m−1). A compensating gate-drain capacitor CGD-1 a is formed inan area where the second extended portion 117-1E2 overlaps with the gatebus line 112(m−1). On the other hand, the drain extension line 117-2includes a first extended portion 117-2E1 that forms the storagecapacitor CS2A of the sub-picture element SP2 and a second extendedportion 117-2E2 that overlaps with a gate bus line 112(m+1). Acompensating gate-drain capacitor CGD-2 a is formed in an area where thesecond extended portion 117-2E2 overlaps with the gate bus line112(m+1).

Comparing the blue picture element (i.e., the (m, n+1) picture element)to the other picture element (i.e., the (m, n) picture element), it canbe seen that the capacitance value (or the area shown in FIG. 14) of thestorage capacitor CS1A is greater the (m, n) picture element than in the(m, n+1) picture element. It can also be seen that the compensatinggate-drain capacitors CGD-1 a and CGD-2 a are provided only for the (m,n+1) picture element. That is to say, the compensating gate-draincapacitors CGD-1 a and CGD-2 a are provided to compensate for thedeficit in the capacitance value of the storage capacitor CS1A of the(m, n+1) picture element with the (m, n) picture element.

It should be noted that both of the (m, n) and (m, n+1) picture elementshave the gate-drain capacitors CGD-1 b and CGD-2 b. These are capacitorsformed between the extended portion of the gate bus line (m) to drivethe (m, n) picture element and the drain extension line 117-1 or 117-2.That is why their capacitance value is included in Cgd in the numeratorof the equation that defines ΔVd and these capacitors are provided toadjust the Cgd value.

Thus, by adopting the configuration of the liquid crystal display device300A, the ΔVd values can be equalized in every color picture elementwith a simpler configuration than that of the liquid crystal displaydevice 200A.

Furthermore, in the example illustrated in FIG. 14, the drain extensionlines 117-1 and 117-2 and the extended portion of the gate bus line112(m) are arranged such that the blue picture element (i.e., (m, n+1)picture element in this example) and the other picture element (i.e.,(m, n) picture element in this example) have apertures (i.e., openingsto pass the incoming light) of substantially the same shape. By makingthe shapes of the apertures of all picture elements substantially thesame in this manner, the uniformity of display can be increased. Justlike the liquid crystal display device 200A, the liquid crystal displaydevice 300A also has a structure in which the aperture ratio of a pixelis increased by making the sub-picture element electrodes 111-1 and111-2 overlap with the source bus line 114(n) with an interleveldielectric film interposed between them.

FIG. 15 illustrates a picture element structure for a liquid crystaldisplay device 400A as another preferred embodiment of the presentinvention. The equivalent circuit of the liquid crystal display device400A is the same as that of the liquid crystal display device 100 shownin FIG. 8. In FIG. 15, illustrated schematically are the structure oftwo picture elements that are located at the intersection between them^(th) row and n^(th) column and at the intersection between the m^(th)row and (n+1)^(th) column on the TFT substrate, among multiple pictureelements that are arranged in column and rows. The picture element atthe intersection between the m^(th) row and n^(th) column is either ared picture element or a green picture element, while the pictureelement at the intersection between the m^(th) row and (n+1)^(th) columnis a blue picture element. In this liquid crystal display device 400A,each picture element P includes a first sub-picture element SP1 and asecond sub-picture element SP2. That is to say, this liquid crystaldisplay device 400A has the multi-picture element structure shown inFIG. 1 and the ratio in the area of the first sub-picture element SP1 tothe second sub-picture element SP2 is one to one.

In the liquid crystal display device 400A, by setting the capacitancevalues (or the areas) of the storage capacitors CS1 and CS2 of the bluepicture element (i.e., the (m, n+1) picture element) to be smaller thanthose of the storage capacitors CS1 and CS2 of the other color pictureelement (i.e., the (m, n) picture element), the ΔVα value of the bluepicture element can be smaller than that of the other color pictureelement.

ΔVd can be regulated by adjusting Cgd (e., the numerator of the equationthat gives ΔVd) of the TFT.

As shown in FIG. 15, in the TFT 116-1, the areas of overlap of the drainelectrodes 116-1Da and 116-1Db with the gate electrode 116-1G aregreater in the (m, n) picture element than in the (m, n+1) pictureelement. In the same way, in the TFT 116-2, the areas of overlap of thedrain electrodes 116-2Da and 116-2Db with the gate electrode 116-2G aregreater in the (m, n) picture element than in the (m, n+1) pictureelement. That is why the Cgd capacitance value of the TFT 166-1 of the(m, n) picture element is greater than that of the TFT 166-1 of the (m,n+1) picture element by those extra areas of overlap of the drainelectrodes (corresponding to CGD-1 a and CGD-1 b) with the gateelectrode. In the same way, the Cgd capacitance value of the TFT 166-2of the (m, n) picture element is greater than that of the TFT 166-2 ofthe (m, n+1) picture element by those extra areas of overlap of thedrain electrodes (corresponding to CGD-2 a and CGD-2 b) with the gateelectrode. And by ironing out such a difference in Cgd capacitancevalue, the difference in the capacitance value of the storage capacitorcan be compensated for.

By adopting such a configuration, every picture element will have thesame structure except the TFT section thereof, and therefore, everypicture element will have an aperture of the same shape and a highdegree of uniformity of display will be achieved. Just like the liquidcrystal display devices 200A and 300A described above, the liquidcrystal display device 400A also has a structure in which the apertureratio of a pixel is increased by making the sub-picture elementelectrodes 111-1 and 111-2 overlap with the source bus line 114(n) withan interlevel dielectric film interposed between them.

FIG. 16 illustrates a picture element structure for a liquid crystaldisplay device 500A as another preferred embodiment of the presentinvention. The equivalent circuit of the liquid crystal display device500A is the same as that of the liquid crystal display device 100 shownin FIG. 8. In FIG. 16, illustrated schematically are not only thestructure of two picture elements that are located at the intersectionbetween the m^(th) row and n^(th) column and at the intersection betweenthe m^(th) row and (n+1)^(th) column on the TFT substrate, amongmultiple picture elements that are arranged in column and rows, but alsothe arrangement of ribs on the counter substrate. The picture element atthe intersection between the m^(th) row and n^(th) column is either ared picture element or a green picture element, while the pictureelement at the intersection between the m^(th) row and (n+1)^(th) columnis a blue picture element. In this liquid crystal display device 500A,each picture element P includes a first sub-picture element SP1 and asecond sub-picture element SP2. That is to say, this liquid crystaldisplay device 500A has the multi-picture element structure shown inFIG. 1 and the ratio in the area of the first sub-picture element SP1 tothe second sub-picture element SP2 is one to one.

The liquid crystal display device 500A is an MVA mode LCD, in which eachof the sub-picture element electrodes 111-1 and 111-2 has slits as shownin FIG. 16 and in which liquid crystal molecules are aligned in apredetermined direction by an oblique electric field generated near theslits and an anchoring force produced by the ribs that have been formedon the surface of the counter substrate in contact with the liquidcrystal layer. Specifically, those slits and ribs are arranged so as toform four liquid crystal domains, where liquid crystal molecules havefour tilt angles that are different from each other by 90 degrees uponthe application of a voltage, in each of the sub-picture elements SP1and SP2. Although the slits and ribs do not have to be aligned in such apattern, each sub-picture element preferably has four liquid crystaldomains to improve the viewing angle characteristic.

In the liquid crystal display device 500A, by setting the areas of thesub-picture element electrodes 111-1 and 111-2 of the blue pictureelement (i.e., the (m, n+1) picture element) to be smaller than those ofthe sub-picture element electrodes 111-1 and 111-2 of the other colorpicture element (i.e., the (m, n) picture element), the capacitancevalues of the liquid crystal capacitors Clc1 and Clc1 and the storagecapacitors Ccs1 and Ccs2 (see FIG. 8) of the blue picture element can besmaller than those of the other color picture element.

This is a structure to be adopted in a situation where the interleveldielectric film is relatively thin. In this structure, the sub-pictureelement electrodes 111-1 and 111-2 are arranged so as not to overlapwith the source bus line 114(n). Also, most of the storage capacitorsCS1 and CS2 is defined by providing extended portions 113-1E and 113-2E,which run parallel to the source bus line 114(n), for the CS bus lines113-1 and 113-2 and by making the CS bus lines 113-1 and 113-2,including parts of the extended portion 113-1E and 113-2E, overlap withthe sub-picture element electrodes 111-1 and 111-2 with an interleveldielectric film (not shown) interposed between them. In this example,each of the CS bus lines 113-1 and 113-2 includes a pair of extendedportions 113-1E, 113-2E that overlaps with both edges of its associatedsub-picture element electrode 111-1 or 111-2. However, the presentinvention is in no way limited to this specific preferred embodiment.Also, the thickness of the interlevel dielectric film may beappropriately adjusted according to its dielectric constant and area. Itshould be noted that overlapping portions between the extended portions117-1E and 117-2E of the drain extension lines 117-1 and 117-2 and theCS bus lines 113-1 and 113-2 also contribute to forming the storagecapacitors.

In the liquid crystal display device 200A, etc. described above, onlythe capacitance value of the storage capacitor CS is adjusted to makethe ΔVα value of the blue picture element different from the others. Inthis liquid crystal display device 500A, however, the capacitance valuesof the liquid crystal capacitor Clc and the storage capacitor CS areadjusted. If the area of the sub-picture element electrode is reduced,the capacitance values of the liquid crystal capacitor Clc and storagecapacitor CS will both decrease. But as the capacitance value of thestorage capacitor CS decreases significantly, the ΔVα value can bereduced eventually.

In the liquid crystal display device 500A, ΔVd is regulated by adjustingCgd (i.e., the numerator of the equation that gives ΔVd) of the TFT, asin the liquid crystal display device 400A described above. As shown inFIG. 16, in this liquid crystal display device 500A, the areas of thedrain electrodes 116-1D and 116-2D of the TFTs 116-1 and 116-2 areincreased in the (m, n) picture element compared to the (m, n+1) pictureelement, and the areas of the source electrodes 116S are increased, too.By adopting such a configuration, the Cgd capacitance value of the (m,n) picture element can be increased and the channel width of the TFT canalso be increased effectively.

FIG. 17 illustrates a picture element structure for a liquid crystaldisplay device 600A as another preferred embodiment of the presentinvention. The equivalent circuit of the liquid crystal display device600A is the same as that of the liquid crystal display device 100 shownin FIG. 8. In FIG. 17, illustrated schematically are not only thestructure of two picture elements that are located at the intersectionbetween the m^(th) row and n^(th) column and at the intersection betweenthe m^(th) row and (n+1)^(th) column on the TFT substrate, amongmultiple picture elements that are arranged in column and rows, but alsothe arrangement of ribs on the counter substrate. FIG. 18A is across-sectional view of the device as viewed on the plane 18A-18A′ shownin FIG. 17, and FIG. 18B is a cross-sectional view of the device asviewed on the plane 18B-18B′ shown in FIG. 17.

The liquid crystal display device 600A is an MVA mode LCD having thesame alignment division structure as the liquid crystal display device500A. The picture element at the intersection between the m^(th) row andcolumn is either a red picture element or a green picture element, whilethe picture element at the intersection between the m^(th) row and(n+1)^(th) column is a blue picture element. In this liquid crystaldisplay device 600A, each picture element P includes a first sub-pictureelement SP1 and a second sub-picture element SP2. That is to say, thisliquid crystal display device 600A has the multi-picture elementstructure shown in FIG. 1 and the ratio in the area of the firstsub-picture element SP1 to the second sub-picture element SP2 is one toone.

Just like the liquid crystal display device 500A, the liquid crystaldisplay device 600A also includes a relatively thin interleveldielectric film 126 between the source bus line 114(n) and thesub-picture element electrodes 111-1 and 111-2 (see FIGS. 18A and 18B).That is why the sub-picture element electrodes 111-1 and 111-2 arearranged so as not to overlap with the source bus line 114(n).Furthermore, the liquid crystal display device 600A includes not justthe gate insulating film 122 of the liquid crystal display device 200Aand other devices described above but also a spin-on-glass (SOG) film121 on the gate insulating film 122. As the material of the SOG film, aspin-on-glass material including an organic component (i.e., so-called“organic SOG material”) is preferably used. Among other things, a SOGmaterial with a Si—O—C bond as its skeleton or a SOG material with aSi—C bond as its skeleton can be used particularly effectively. As usedherein, the SOG material is a material that can form a glass film (i.e.,a silica-based coating) by spin coating or any other suitable coatingprocess.

The SOG film 121 is relatively thick. For that reason, if the SOG film121 were interposed between the semiconductor layer 123 of the TFT (seeFIG. 18A) and the gate electrode 112(m), then the TFT would not operatenormally. To avoid such a situation, the SOG film 121 is not provided ina region of the TFT 116-1 or 116-2 where the gate insulating film 122should function as such. In FIGS. 17 and 18A, that region is shown as aSOG film removed region 118T.

Also, the SOG film 121 has a relatively low dielectric constant of fouror less, for example. That is why if the SOG film 121 is arrangedbetween the electrodes, then the capacitance value of the capacitor tobe formed will be small. For example, in the arrangement shown in FIG.18C, the SOG film 121 is interposed between the CS bus line 113-1 andthe sub-picture element electrodes 111-1 and 111-2. That is why thecapacitor to be formed between those electrodes will have a smallcapacitance value and will contribute a little to forming a storagecapacitor.

In the liquid crystal display device 600A, the SOG film removed regions118C1 and 118C2 are defined between the drain extension line extendedportions 117-E1 and 117-E2 and the CS bus lines 113-1 and 113-2 as shownin FIGS. 17 and 18B, thereby forming storage capacitors. Specifically, astorage capacitor CS1 is formed in the SOG film removed region 118C1 anda storage capacitor CS2 is formed in the SOG film removed region 118C2.

In the liquid crystal display device 600A, by setting the capacitancevalues of the storage capacitors CS1 and CS2 of the blue picture element(i.e., the (m, n+1) picture element) to be smaller than those of thestorage capacitors CS1 and CS2 of the other color picture element (i.e.,the (m, n) picture element), the ΔVα value of the blue picture elementcan be smaller than that of the other color picture element.

ΔVd is regulated by adjusting Cgd (i.e., the numerator of the equationthat gives ΔVd) of the TFT, as in the liquid crystal display devices400A and 500A described above. Also, as in the liquid crystal displaydevice 500A, the areas of the drain electrodes 116-1D and 116-2D of theTFTs 116-1 and 116-2 are increased in the (m, n) picture elementcompared to the (m, n+1) picture element, and the areas of the sourceelectrodes 116S are increased, too. By adopting such a configuration,the Cgd capacitance value of the (m, n) picture element can be increasedand the channel width of the TFT can also be increased effectively.

The method of regulating ΔVd by adjusting Cgd may be modified in variousmanners. According to the TFT configuration, any appropriate one may beselected from those various methods, or if necessary, two or moremethods may be combined, too. Some of those modified methods ofadjusting Cgd of a TFT are shown in FIGS. 19( a) through FIG. 19( g).

First, in the TFT section 70A shown in FIG. 19( a), Cgd of a colorpicture element other than a blue picture element is increased byextending the drain electrodes 116-1D and 116-2D.

On the other hand, in the TFT section 70B shown in FIG. 19( b), Cgd of acolor picture element other than the blue picture element is increasedand the channel width of the TFT is increased effectively by extendingthe drain electrodes 116-1D and 116-2D and the source electrode 116S.

These methods can be carried out just as described above. Other optionsare available as shown in FIGS. 19( c) through 19(g).

Specifically, in the TFT section 70C shown in FIG. 19(c), Cgd of thecolor picture element other than the blue picture element is increasedby extending the drain electrode 116-1D. And by extending the drainelectrode in the direction in which the gate bus line runs, the decreasein aperture ratio is minimized.

On the other hand, in the TFT section 70D shown in FIG. 19( d), not justCgd of the color picture element other than the blue picture element butalso the channel width the TFT are increased effectively by extendingthe source electrode 1165, as well as the drain electrode 116-1D. And byextending the channel width of the TFT in the direction in which thegate bus line runs, the decrease in aperture ratio is minimized.

Furthermore, in the TFT section 70E shown in FIG. 19( e), CGD-1 isformed with the tip of the drain electrode 116D extended, therebyincreasing not only Cgd of the color picture element other than the bluepicture element but also the vertical channel width of the TFT. Sincethe shape of the source electrode 116S is not changed, the load on thesource bus line 114 hardly increases.

Meanwhile, in the TFT section 70F shown in FIG. 19( f), not just Cgd ofthe color picture element other than the blue picture element but alsothe channel width of the TFT are increased effectively by extending thedrain electrodes 116-1D and 116-2D. Since the shape of the sourceelectrode 116S is not changed, the load on the source bus line 114hardly increases.

Furthermore, in the TFT section 70G shown in FIG. 19( g), not just Cgdof the color picture element other than the blue picture element butalso the channel width of the TFT are increased even more effectivelythan in the TFT section 70F by extending the source electrodes 116S1 and116S2, as well as the drain electrodes 116-1D and 116-2D.

Optionally, the configuration of the liquid crystal display device 700Ashown in FIG. 20 may also be adopted.

The liquid crystal display device 700A basically has the sameconfiguration as the liquid crystal display device 200A shown in FIG.12. In the liquid crystal display device 200A, two storage capacitorsare provided for each sub-picture element (e.g., the storage capacitorsCS1A and CS1B are provided for the sub-picture element SP1) and theircapacitance values are changed between the blue picture element and theother color picture element, thereby making their ΔVα different fromeach other. On the other hand, in the liquid crystal display device700A, each sub-picture element also includes two storage capacitors(e.g., the storage capacitors CS1A and CS1B are provided for thesub-picture element SP1) but the capacitance values of these storagecapacitors are the same in every color picture element. In the liquidcrystal display device 700A, the drain extension line 117-1 for thefirst sub-picture element SP1 of the blue picture element (i.e., the (m,n+1) picture element) and the drain extension line 117-2 for the secondsub-picture element SP2 thereof are short-circuited together with adrain short-circuit line 117-3, thereby reducing ΔVα of the blue pictureelement to substantially zero. That is to say, since only the bluepicture element does not have the multi-picture element structure, theviewing angle dependence of the blue grayscale characteristic willdeteriorate but problems that would otherwise be caused by coloring or avariation in ΔVd will never happen.

Any of these configurations that have been described with reference toFIGS. 12 through 19, but the one shown in FIG. 20, may be used either byitself or in any arbitrary combination with another one or other ones.

FIG. 21 shows the grayscale dependences of ΔVd of respective colorpicture elements in a liquid crystal display device as a preferredembodiment of the present invention. The graph shown in FIG. 21 showsΔVd of the respective color picture elements in a situation where theratio X of the capacitance value of the storage capacitor of the bluepicture element to that of the storage capacitor of the other colorpicture elements is optimized to be 0.56 in order to minimize the shifttoward the yellow range at an oblique viewing angle in the liquidcrystal display device that has already been described with reference toFIG. 10. Specifically, the curve L(B) shows ΔVd of the blue pictureelement, the curve L′(R, G) shows ΔVd of the other color pictureelements, of which the difference in storage capacitance value is notcompensated for, and the curve L(R, G) shows ΔVd of the other colorpicture elements that has been substantially equalized with that of theblue picture element by adjusting Cgd.

As can be seen clearly from FIG. 21, if X=0.56 and if the difference instorage capacitance is not compensated for at all, then the differencein ΔVd between the blue picture element and the other color pictureelements exceeds 0.5 V (=500 mV). The present inventors discovered andconfirmed via experiments that when the difference in ΔVd exceeded 150mV, a flicker was produced and the reliability decreased. If thedifference in ΔVd exceeds 50 mV, then sometimes a degradation may berecognized in display quality. That is why to avoid the problems to becaused by the ΔVd difference in actual products, ΔVd should be reducedto 50 mV or less in at least one grayscale. In this description, if ΔVdis substantially the same, it means that the difference in ΔVd is equalto or smaller than 50 mV. It can be seen that in the example illustratedin FIG. 21, the difference between the curve L(B) and the curve L(R, G)at the 140^(th) grayscale is as small as 4 mV.

A multi-picture element structure in which each picture element is splitinto two sub-picture elements has been described as a preferredembodiment of the present invention. However, the present invention isin no way limited to that specific preferred embodiment. Alternatively,each picture element may also be divided into three or more sub-pictureelements as well.

INDUSTRIAL APPLICABILITY

A liquid crystal display device according to the present invention canbe used effectively in liquid crystal TVs and other applications thatrequire excellent viewing angle characteristics.

1. A liquid crystal display device comprising a plurality of pictureelements that are arranged in columns and rows so as to form a matrixpattern, each said picture element including a liquid crystal layer anda plurality of electrodes for applying a voltage to the liquid crystallayer, wherein each said picture element includes a first sub-pictureelement and a second sub-picture element having the ability to applymutually different voltages to their liquid crystal layer, wherein at agrayscale level, the first sub-picture element has a higher luminancethan the second sub-picture element, and wherein each of the first andsecond sub-picture elements includes a liquid crystal capacitor formedby a counter electrode and a sub-picture element electrode that facesthe counter electrode through the liquid crystal layer, and at least onestorage capacitor, each being formed by a storage capacitor electrodethat is electrically connected to the sub-picture element electrode, aninsulating layer, and a storage capacitor counter electrode that isopposed to the storage capacitor electrode with the insulating layerinterposed between them, and wherein after a display voltagerepresenting a certain grayscale level has been applied to therespective sub-picture element electrodes of the first and secondsub-picture elements, a voltage difference ΔVα is produced betweenvoltages to be applied to the respective liquid crystal capacitors ofthe first and second sub-picture elements by way of their associatedstorage capacitor(s), and wherein in some of the picture elements, thevoltage difference ΔVα changes from one picture element to another. 2.The liquid crystal display device of claim 1, wherein the pictureelements include a plurality of color picture elements that representmutually different colors and that include a blue picture element and/ora cyan picture element, and wherein among those color picture elements,the ΔVα value of the blue and/or cyan picture element(s) is thesmallest.
 3. The liquid crystal display device of claim 1, wherein theat least one storage capacitor includes only one storage capacitor, andwherein the counter electrode is a single electrode that is provided incommon for the first and second sub-picture elements, the storagecapacitor counter electrodes of the first and second sub-pictureelements are electrically independent of each other, and the waveformsof storage capacitor counter voltages to be supplied through storagecapacitor lines that are associated with the storage capacitor counterelectrodes are different between the first and second sub-pictureelements, and wherein in some of the picture elements, the storagecapacitors have different capacitance values.
 4. The liquid crystaldisplay device of claim 3, wherein the picture elements include aplurality of color picture elements that represent mutually differentcolors and that include a blue picture element and/or a cyan pictureelement, and wherein among those color picture elements, the capacitancevalue of the storage capacitor of the blue and/or cyan pictureelement(s) is the smallest.
 5. The liquid crystal display device ofclaim 4, wherein the color picture elements further include a redpicture element and a green picture element, and wherein supposing thecapacitance values of the storage capacitors of the blue and/or cyanpicture element(s), the green picture element, and the red pictureelement are identified by C_(CS-B), C_(CS-C), C_(CS-G) and C_(CS-R),respectively, the inequality C_(CS-B)≦C_(CS-C)<C_(CS-G)≦C_(CS-R) issatisfied.
 6. The liquid crystal display device of claim 2, wherein theat least one storage capacitor includes only one storage capacitor, andwherein the counter electrode is a single electrode that is provided incommon for the first and second sub-picture elements, the storagecapacitor counter electrodes of the first and second sub-pictureelements are electrically independent of each other, and the waveformsof storage capacitor counter voltages to be supplied through storagecapacitor lines that are associated with the storage capacitor counterelectrodes are different between the first and second sub-pictureelements, and wherein in some of the picture elements, the liquidcrystal capacitors have different capacitance values.
 7. The liquidcrystal display device of claim 1, further comprising gate bus lines,source bus lines and TFTs, wherein each of the first and secondsub-picture elements includes a TFT that is connected to the sub-pictureelement electrode thereof, and wherein one of the picture elements thathas the smallest voltage difference ΔVα further includes a storagecapacitor that has been formed between the picture element's row and thegate bus line of its adjacent row.
 8. The liquid crystal display deviceof claim 1, further comprising gate bus lines, source bus lines andTFTs, wherein each of the first and second sub-picture elements includesa TFT that is connected to the sub-picture element electrode thereof,and wherein the gate-drain capacitance Cgd of the TFT of one of thepicture elements that has the smallest voltage difference ΔVα is smallerthan that of the TFT of any other picture element.
 9. The liquid crystaldisplay device of claim 1, wherein the liquid crystal layer is avertical alignment liquid crystal layer and contributes to conducting adisplay operation in normally black mode.
 10. The liquid crystal displaydevice of claim 1, wherein the at least one storage capacitor includestwo storage capacitors, and wherein the counter electrode is a singleelectrode that is provided in common for the first and secondsub-picture elements, and wherein the storage capacitor counterelectrodes of the two storage capacitors of the first sub-pictureelement are electrically independent of each other, and the storagecapacitor counter electrodes of the two storage capacitors of the secondsub-picture element are also electrically independent of each other. 11.The liquid crystal display device of claim 10, wherein if the twostorage capacitors of the first sub-picture element are identified byCS1A and CS1B and if the two storage capacitors of the secondsub-picture element are identified by CS2A and CS2B, the storagecapacitor counter electrodes of the storage capacitors CS1A and CS2B areelectrically connected to the same first storage capacitor line, thestorage capacitor counter electrodes of the storage capacitors CS1B andCS2A are electrically connected to the same second storage capacitorline, and the first and second storage capacitor lines are electricallyindependent of each other.
 12. The liquid crystal display device ofclaim 11, wherein if the capacitance values of the storage capacitorsCS1A, CS1B, CS2A and CS2B are identified by Ccs1A, Ccs1B, Ccs2A andCcs2B, respectively, and if Ccs1α=Ccs1A−Ccs1B and Ccs2α=Ccs2A−Ccs2B,some of the picture elements have different Ccs1α or Ccs2α.
 13. Theliquid crystal display device of claim 12, wherein the picture elementsinclude a plurality of color picture elements that represent mutuallydifferent colors and that include a blue picture element and/or a cyanpicture element, and wherein among those color picture elements, theCcs1α and Ccs2α values of the blue and/or cyan picture element(s) arethe smallest.
 14. The liquid crystal display device of claim 12, whereinif Ccs1β=Ccs1A+Ccs1B and Ccs2β=Ccs2A+Ccs2B, the Ccs1β and Ccs2β valuesremain the same in every picture element.